Exploring the enhancement effects of hetero-metal doping in CeO2 on CO2 photocatalytic reduction performance

Doping hetero-metal ions in semiconductors, especially metal oxides, is a common practice to elevate their photocatalytic reduction activity. However, the underlying enhancement mechanism of doping different metal ions into the host lattice on photocatalytic CO2 reduction has been rarely explored and thus remains unclear. In this work, CeO2 nanoparticles doped with three different metal ions (CeM, M = Y, La, Mo) have been synthesized, which exhibited significantly improved photo-reduction CO2 activity. According to the analysis of Electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS), Y and Mo doping results in increased oxygen vacancy concentration in CeO2, which promotes the absorption of UV–visible light and the separation/transfer of electrons and holes, consequently elevating the catalytic activity. More importantly, through in-situ FT-IR, CO2 adsorption/activation and the intermediates generated on catalyst surface during CO2 photoreduction reaction were investigated and discussed in-depth. Similar carbonates and hydrocarbonates, such as HCO3−, b-CO32− and m-CO32−, have been found to be produced on CeO2 and CeM, while these intermediates accumulated and strongly covered on the catalyst surface have been revealed to be responsible for the gradually declined CO2 reduction activity and stability.